When the JumpCon fraud happened ((I lost $465, thank you!)) in some of the later court filings, it had the amounts owed to various actors for their appearance fee. The original article seems to be gone, but someone reporting on it has two of the figures preserved...
http://www.conventionscene.com/2009/05/25/jumpcon-owner-files-for-bankruptcy/
Edward James Olmos @ $60,000
Stephen Furst @ $1500
I also remember from when I originally read it, Bob Picardo @ 8,000 and J.G. Hertzler @ $2000 or 3000.
I'd always guessed at the figures myself, and I was pleased to find I'd been pretty accurate at my guesstimates.
I know at one point back in the day, Creation tried to get Harrison Ford to do a convention. They offered him their entire budget of $200,000 and that didn't even leave enough for any autographs. He still rejected it. $200 G's to talk for an hour on stage, lol.
Some folks like Shatner, Nimoy, Stewart can still pull down the big numbers even when they're appearing more often than normal. Stewart in the late 90s/early 00s was pretty rare, less than one a year. Now he's doing 2, sometimes 3 or 4 a year.
And back in the 'old' days of as recently as the early 00s, some of them where able to get away with not signing in person. You'd be provided with a pre-signed 8x10 at the show. As was the case when I first met Stewart in 2000. He's since done two purely autograph shows in my area, and I've gotten most of my "must have" items signed by him in person including a Locutus of Borg photo.

It was the repugnant David Scott of Slanted Fedora infamy that changed that; he made them all sign in person, and it eventually forced Creation to follow suit as people where no longer willing to accept the pre-signing nonsense once Scott had gotten people like Shatner to sign like everyone else. I hate that man (David Scott) but he did some good things for the convention scene in his brief reign as king. He was also a scumbag and a cheat...
Something else that can determine how much you make is the $ amount you charge for autographs. When doing purely autograph shows, bigger names like Olmos and Stewart tend to charge bigger fees. Recently, Stewart was charging $60 a pop, Olmos $50. It can deter some fans. I bite the bullet. Olmos was really great to me though; I had come prepared with 8 photos I wanted him to sign, and he cut his price from $50 to $30 if he could personalize them (which I imagine was to make sure they where not going out on e-Bay, lol) -- so for paying LESS money, I got 8 items PERSONALIZED which you normally pay MORE for. Hehe. He rocks though. He was very patient and friendly. I had a bunch of inscriptions I'd wanted, famous lines. He did them all and we had a nice chat for about 10 minutes. One of the better experiences.
